1. Field of the Invention
This invention relates to the recovery of methane (natural gals) by sub-sea mining of clathrates.
2. Description of the Art Practices
U.S. Pat. No. 5,660,603 issued to Elliot et al., Aug. 26,1997 discusses a process for separating components of gas mixtures which have different hydrate forming characteristics using an aqueous liquid to absorb one of the gases preferentially by attaining conditions slightly above the catastrophic point at which gas hydrates form. Specifically, the separation of gas mixtures containing light hydrocarbons and carbon dioxide is accomplished without significantly reducing the pressure of the carbon dioxide or without requiring significant amounts of heat energy for regeneration.
U.S. Pat. No. 5,473,904 issued Dec. 12, 1995 to Guo et al., discloses a method of forming clathrate hydrates further by pressurizing a hydrate-forming gas, cooling liquid water below the gas-water-hydrate equilibrium curve, combining the hydrate-forming gas and the liquid water while locally supercooling the gas, and thereby forming a clathrate hydrate.
U.S. Pat. No. 4,376,462 issued Mar. 15, 1983 to Elliott et al., describes a method and apparatus for producing gaseous hydrocarbons from formations comprising solid hydrocarbon hydrates located under either a body of land or a body of water. In the Elliott et al., process warm brine or water brought down from an elevation above that of the hydrates, through a portion of the apparatus, passes in contact with the hydrates and melts them. The liquid then continues up another portion of the apparatus, carrying entrained hydrocarbon vapors in the form of bubbles, which can easily be separated from the liquid. After a short startup procedure, the process and apparatus are substantially self-powered by virtue of pressure differences. A related disclosure to U.S. Pat. No. 4,376,462 issued Mar. 15, 1983 to Elliott et al., is found in Elliott et al., in U.S. Pat. No. 4,424,858 issued Jan. 10, 1984.
An article in the Journal of Petroleum Geology, vol. 19(1). January 1996, pp. 41-56 OCEANIC METHANE HYDRATES: A "FRONTIER" GAS RESOURCE authored by Max et al., discusses the chemistry of methane hydrates. Max et al., article discloses that methane hydrates are ice-like compounds consisting of natural gas (mainly methane) and water, whose crystal structure effectively compresses the methane; each cubic meter of hydrate can yield over 150 cubic meters of methane. The hydrates cement sediments and impart considerable mechanical strength; the fill porosity and restrict permeability.
An article entitled Methane Hydrate, A Special Clathrate: Its Attributes and Potential by Max et al., dated Feb. 28, 1997 discusses the recovery and processing of methane hydrate. Similar disclosures are also made by Max et al., in an article entitled Oceanic Gas Hydrate: Guidance for Research and Programmatic Development for work done at the Naval Research Laboratory bearing a date of Dec. 31, 1997. Further disclosures are made by Max et al., in a chapter entitled Natural gas hydrates: Arctic and Nordic Sea potential in Arctic Geology and Petroleum Potential edited by T. O. Vorren et al.
The need remains for effective processes to be developed to allow the hydrocarbon gas trapped in the ice like stricture of the clathrate and the sediment to be effectively mined and separated. The present invention deals with one such effective method of the recovery of the hydrocarbon gases from the sea floor.
To the extent that the foregoing references are relevant to the present invention, they are herein specifically incorporated by reference. Measurements herein are stated in degrees of approximation and where appropriate the word "about" may be inserted before any measurement.